“Weed smokers will be punished according to the Korean law, even if they did so in countries where smoking marijuana is legal. There won’t be an exception,” said the official, according to the Korea Times.

The South Korea government also put out a warning last week, the day before Canada legalized marijuana.

On Oct. 16, the South Korean Embassy in Canada said on Twitter: “Even if South Koreans are in a region where marijuana is legal, it will be illegal for them to consume it. Please take care not to commit an illegal act and be punished.”

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Korean police said they plan to hold briefing sessions in Canada and Uruguay (the first country in the world to legalize pot) to explain the risks of smoking marijuana to Korean residents, the Korea Times reported.

“It’s possible that a country could make it an offence … as there are issues of sovereignty there,” said Harrison Jordan, a Toronto-based cannabis lawyer.

“There are certainly other countries who have done so … like Saudi Arabia, (which makes) it illegal to have any THC in your system.”

Japan also gave its residents a warning. On Oct. 4, the Consulate-General of Japan in Vancouver issued a statement saying the possession and purchase of the drug is not only illegal in Japan, but “may be applied … in foreign countries.”

Under South Korea’s narcotics law, selling, buying or consuming marijuana is a crime punishable by up to five years in prison or a fine of up to 50 million won, around $57,000.

The use of marijuana is illegal and considered a serious crime in South Korea. According to Korean media, “marijuana is on the same level of taboo as a hard drug like heroin or crystal meth.”

In July 2017, South Korea pop star T.O.P, was given a suspended 10-month jail sentence for smoking marijuana. The singer was charged after using marijuana four times in October 2016 at his home in the capital, Seoul.

T.O.P, of South Korean boy band Big Bang, arrives at the Seoul Central District Court for hearing on his marijuana usage case on July 20, 2017 in Seoul, South Korea.

Chung Sung-Jun/Getty Images

How will South Korea test for marijuana?

“South Korea can’t screen everyone who visited a foreign country, but the police maintain a blacklist that leads to certain individuals being supervised,” Lee Chang-Hoon, a professor in the department of police administration at Hannam University in Daejeon told the Guardian.

“But the police are more concerned with the transportation of marijuana into South Korea, and the police messaging shows they are anxious about tackling this issue in the near future.”

Around 286,000 South Koreans visited Canada in 2017, according to Statistics Canada.